Welcome,
The underlying issue is that OpenEars’ sound requirements add up to an additional audio engine’s worth of code, so there is probably an unwanted interaction between OpenEars’ audio session handling and SimpleAudioEngine. A search through this forum for “audiosession” and/or “allowmixing” should turn up some explanations of how to turn on mixing for different audio streams/sessions, which would be the first troubleshooting step. This issue:
https://www.politepix.com/forums/topic/openears-avplayer-issue/
Probably has very similar underpinnings, so it is probable worth a read to debug the issue you’re seeing.